Process for making p-nitrochlorobenzene



United States Patent 3,153,674 PRGCESS FOR MAKING p-NTTRGCHLORO- BENZENE David E. Dunlap, St. Louis, Mo., assiwor to Monsanto Company, a corporation of Delaware No Drawing. Filed Jan. 28, 1963, Ser. No. 254,441 3 Claims. (Cl. 260-646) This invention relates to an improved process for the preparation of p-nitrochlorobenzene. More specifically, this invention relates to preparing substantially pure pnitrochlorobenzene from p-chlorobenzene sulfonic acid.

It is reported in the prior art that p-nitrochlorobenzene is produced at water bath temperatures by adding nitrogen -tetroxide to the reaction mixture of chlorobenzene and strong sulfuric acid. According to the prior art, at water bath temperatures, the nitrogen tetroxide reacts with p-chlorobenzene sulfonic acid, replacing the sulfonic acid group with a nitro group. However, attempts to duplicate the teaching of the prior art utilizing solely pchlorobenzenc sulfonic acid and nitrogen tetroxide failed to support the alleged reaction at Water bath temperatures. Specifically, reacting nitrogen tetroxide with substantially pure p-chlorobenzene sulfonic acid at water bath temperatures failed to produce p-nitrochlorobenzene.

It is well known and established that, at water bath temperatures, the reaction between sulfuric acid and chlorobenzene is incomplete. Thus, the reacted mixture includes p-chlorobenzene sulfonic acid, sulfuric acid, and unreacted chlorobenzene. It is equally well known and established that chlorobenzene, in the presence of sulfuric acid at water bath temperatures, reacts with nitrogen tetroxide to form pand o-nitrochlorobenzene. Accordingly, it is apparent that formation of p-nitrochlorobenzene by the addition of nitrogen tetroxide, at water bath temperatures, to the reaction mixture of sulfuric acid and chlorobenzene results from the nitrogen tetroxide reacting with the previously unreacted chlorobenzene.

It has now been found that nitrogen tetroxide with replace the sulfonic acid group in p-chlorobenzene sulfonic acid when reacted at tempeartures considerably above water bath temperatures, and yields substantially pure pnitrochlorobenzene.

It is therefore an object of this invention to provide a new and improved process for the preparation of substantially pure p-nitrochlorobenzene.

It is another object of this invention to provide a new and improved process for utilizing nitrogen tetroxide to replace the sulfonic acid group in p-chlorobenzene sulfonic acid.

Other objects and advantages of the present invention will become apparent from the following description.

According to the present invention, liquid nitrogen tetroxide is slowly added to p-chlorobenzene sulfonic acid at a temperature from about 110 to 180 C., preferably from about 150 to 160 C. It is preferred to utilize an excess of liquid nitrogen tetroxide and to utilize a reaction vessel having means to condense the nitrogen tetroxide which vaporizes during the reaction. The recovered nitrogen tetroxide is then recycled to the reaction vessel. It is equally possible to utilize an appreciable excess of nitrogen tetrom'de and eliminate the means for condensing the vaporized nitrogen tetroxide and the recycling thereof. In either case, the slow addition of liquid nitrogen tetroxide continues until the equilibrium point of the reaction is attained. Simple experimentation at a stated operating temperature will readily ascertain the approximate time required for the reaction to attain equilibrium. The nitrogen tetroxide replaces the sulfonic acid group with a nitro group to yield substantially pure p-nitrochlorobenzene. Conventional means, such as steam or vacuice um distillation, or the addition of water followed by filtration thereof, can be utilized to readily separate the p-nitrochlorobenzene from the p-chlorobenzene sulfonic acid.

The details of the process will be more fully understood by reference to the examples which follow. These examples set forth representative conditions and quantitles of reactants. It should be emphasized that such examples are not to be construed as limiting the scope of this invention, but are solely for the purposes of illustration. It is further understood that one can start with chlorobenzene which is then sulfonated substantially completely to p-chlorobenzene sulfonic acid. However, for the purposes of illustration and simplicity, the examples utilize p-chlorobenzene sulfonic acid as the starting material.

EXAMPLE I A suitable reaction vessel is charged with 9.6 grams of technical p-chlorobenzene sulfonic acid monohydrate. The vessel contents are heated to between 150 and 180 C. and held there while an excess of liquid nitrogen tetroxide is slowly and continuously added, in increments, over a period of about minutes. The reaction vessel and contents are cooled and thereafter poured into 75 ml. of cold water. A white solid forms which is separated from the aqueous reaction solution by filtration, washed, and thereafter dried. There is obtained 0.25 gram of the white solid showing a MP. of 798l C. Infrared analysis shows the white solid to be p-nitrochlorobenzene of 97.5% purity.

EXAMPLE II The procedure of Example I is followed, except the reaction temperature utilized ranges from about to 170 C., and the nitration period is about minutes. A yield of 18.3% of theory of p-nitrochlorobenzene is obtained.

EXAMPLE 1H The procedure of Example I is followed, except the reaction temperature is from to 180 C., and the nitration period is about 75 minutes. A yield of 34% p-nitrochlorobenzene is obtained.

Employing the procedures set forth in Examples I, II and III, the following table lists the reaction conditions utilized in other nitrations of p-chlorobenzene sulfonic acid to p-nitrochlorobenzene. In each example, the starting material is technical p-chlorobenzene sulfonic acid monohydrate, which may be dehydrated and/ or recrystallized prior to the addition of the nitrogen tetroxide. However, the net amount of anhydrous p-chlorobenzene sulfonic acid present in each sample is substantially equal. Also, an excess of the nitrogen tetroxide is utilized in each example.

Table 1 Temp Percent Yield Example Recycle Time Range, p-NCB (based N 04 (Minutes) C. on charged p-CB SA) Yes- 165 110-120 8. 5 Yes. 130 -190 5 Yes. 75 -190 18 Yes. 60 145-165 7 No 45 1 13-172 9. 2 Yes- 95 135-170 25 Yes 110 130-160 27 N0. 110 140-180 14. 7 Yes 105 160-180 15. 2

- No 135-150 30 Yes. 390 130-160 30-35 (est.)

' 38% based on N 04 used.

While this invention has been described with respect to certain embodiments, it is not so limited, and it is 3 to be understood that variations and modifications thereof obvious to those skilled in the art can be made Without departing from the spirit or scope thereof.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for the preparation of p-nitrochlorobenzene which comprises adding nitrogen tetroXide to pchlorobenzene sulfonic acid at a temperature of from about 110 to 180 C.

2. The process of claim 1 wherein said nitrogen tetroxide is added as a liquid.

3. The process of claim 1 wherein an excess of liquid nitrogen tetroxide is added, and said reaction temperature is from about 150 to 160 C.

No references cited. 

1. A PROCESS FOR THE PREPARATION OF P-NITROCHLOROBENZENE WHICH COMPRISES ADDING NITORGEN TETROXIDE TO PCHLOROBENZEN SULFONIC ACID AT A TEMPERATURE OF FROM ABOUT 110* TO 180*C. 